1. Field of the Invention
This invention relates to security systems for preventing, or rendering very difficult, unauthorized access to the stored liquid contents of a liquid storage tank.
2. Background of the Invention
With the trend toward depletion of liquid fossil fuel resources, the value of crude oil has substantially increased. Such, indeed, is the present value of crude oil as it is produced at the lease and there stored pending removal to a refinery or other remote facility, that larceny of the contents of these storage tanks is rife.
Generally, lease located storage tanks provided for the storage or custody of oil and distillate produced at the well head have sufficient capacity to impound a large volume of, for example, from 100 to 5,000 barrels of liquid hydrocarbon. Authorized removal of the tank contents has been accomplished by the use of a discharge pipe which extends from an internal lower portion of the tank horizontally outwardly to a valve at or near the outer end of the discharge pipe. Tank trucks or other transportation means can be coupled to the discharge pipe when the valve provided in the discharge pipe on the outside of the tank has been opened.
Before the increase in oil prices, relatively straightforward or simple locks on the valves apparently were adequate to prevent significant theft of the liquid contents of the tanks; or blind flanges, caps or other suitable closure devices were used and were sufficient to deter theft.
With the dramatic increase in the value of crude oil and distillate, the audacity of oil theives has proportionately increased and ingenious schemes for larceny of the oil have been devised. Moreover, the difficulty and expense of continuously and adequately surveilling the tanks have enabled the practice of more destructive methods of theft in which, for example, the discharge pipes are sawed off or destroyed above the valve closing them, or other equally destructive methods of obtaining access to the contents of the tank have been used by unauthorized personnel.